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Thread: Buell XB12S runs rough after spark plug change

  1. #1
    Senior Member
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    Apr 2011
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    445
    Hello All:
    I recently changed out the spark plugs on my 2005 XB12S for 10R12APP gapped to 0.035". Ever since, my bike has been running very rough at idle, seemingly misfires constantly. I plugged in Ecmspy and I have no CELs for misfires (not sure the Lightning even has misfire codes). I pulled the spark plugs, re-checked the gap (they were good) and wire connections (good). The bike still ran rough. I haven't performed a TPS reset recently, but I did notice that my TPS had to be at 5.9-6.3% for the bike to idle at 800-1030 RPM. Any ideas??

  2. #2
    Senior Member
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    May 2011
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    I haven't had much luck with H-D plugs myself. I switched to ngk and haven't had a problem. Might check timing. And be sure that wires into and out of the ignition coil are secure.

  3. #3
    Senior Member
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    May 2009
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    326
    Check for the spark plug wires are securely on plug and coil, might be loose contact.

  4. #4
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    I haven't performed a TPS reset recently, but I did notice that my TPS had to be at 5.9-6.3% for the bike to idle at 800-1030 RPM. Any ideas??
    I'd do a reset just to be safe and thorough.

  5. #5
    Senior Member
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    Thanks for the replies. I just did a TPS reset, same issue. I have to adjust the TPS to 6.3% to get a constant tick; but even then the idle varies between 800-1100 RPM. I could check timing, but it's interesting that there was no issue present before the plugs were changed...

  6. #6
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    I think later today I'm going to pull the plugs, check the color again (see if I'm running rich or lean). In my experience with cars - presumably the same with bikes - white powdered plugs would indicate I'm running lean while black oily plugs indicate I'm running rich. I suppose since I have a rough idle that the former would indicate a fueling issue while the latter an electrical issue. I think I'm also going to pick up some dielectric grease and redo the connections.


    Thanks for everyones' help

  7. #7
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    Is it typical that residual oil be present on the timing plug?

  8. #8
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    May 2011
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    Yes...like golden brown color?

  9. #9
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    @C818919

    I suppose. The color of the oil is similar to the color of oil blow-by when I empty the catchcan in my Rex...

  10. #10
    Senior Member
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    Mar 2011
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    1,138
    i had the same problem with ngk plug number dcpr8e ,the bike popped while idle,cough when rolling into throttle and the decel pop was rediculus.i changed to ngk dcpr9eix and it runs perfect now.i dont know if its due to perfomance mods but i have d&D pipe race ecm piper cross air filter and breather reroute. hope this helps



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